When a male toadfish lying in the mud starts humming a love song to a female or grunting a threat to another male, he’s not only playing the mating game; he’s also giving humans a hint of the origins of language.

Researchers studied the brains of the rare vocalizing toadfish as well as its close relative, the midshipman fish, to see which neurons controlled their production of various sounds. They found the answer in a clump of of neurons that are shared by all vertebrates, suggesting that the ability to vocalize evolved around 400 million years ago, before the first fishapods crawled out of the sea. “I’m not saying fish have a language or are using higher powers of the brain,” [said lead researcher Andrew Bass]. “But some of the networks of neurons, nerve cells in the brain, are very ancient” [AP].

Bass explains that the toadfish clearly intend to convey different messages with their various outbursts: “They make different kinds of sounds in different social contexts. Just as birds will use one call to attract a mate and another call to scare a rival off, the fish do exactly the same thing.” A deep hum lures females to a male’s nest; a sharp grunt is used to defend territory [BBC News].

In the study, which will be published tomorrow in the journal Science [subscription required], Bass examined the neurons in the fish’s hindbrain, a region where the back of the brain meets the spinal column. He found that the circuit of neuronscontrolling vocalization in the larval toadfish closely matched the pattern of equivalent neurons in the brains of birds, frogs, amphibians and mammals, including humans. He concluded that this circuit is an shared evolutionary hand-me-down from our last common ancestor. Among different modern groups, there are certainly differences in the network’s complexity, but its basic structure has been remarkably preserved across evolutionary time [Not Exactly Rocket Science].